Sorry, but the target audience isn’t the very general forum of HN, it’s folks who likely know Gleam (given it’s a Gleam conference). Should they have a small explainer link? Maybe, but I don’t think they need to go in depth about it and a link to the language page is enough.
Please note that the person who posted this announcement to HN is the event's organizer. Thus it seems reasonable to conclude that "the very general forum of HN" is part of the event's target audience.
This one should. The whole point of announcements is to cast a wide net in hopes of catching people who are new to the scene, and those new folks shouldn't be expected to already know the scene's lingo.